Balanced Chemical Equations with State Symbols – NCERT Class 10 Science Ch 2 Q3
Balanced Chemical Equations with State Symbols – NCERT Class 10 Science Ch 2 Q3
This is one of those fundamental questions that appears almost every year in CBSE boards – and honestly, it’s basically free marks if you know the format. Let’s make sure you write balanced equations perfectly, with all the state symbols in place.
📌 Quick Answer
Balanced equations with state symbols:
1. BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)
2. NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
Understanding the First Equation: Barium Chloride + Sodium Sulphate
Let’s start with the first reaction:
BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)
This is what we call a double displacement reaction – basically, the positive and negative ions swap partners. When you mix these two solutions in your lab, something interesting happens immediately. You’ll see a white precipitate forming – that’s barium sulphate (BaSO₄) which is insoluble in water.
Now, here’s the important part. Notice the “2” before NaCl? That’s not random. Let me show you why it’s there.
Why Do We Need “2NaCl”?
Let’s count the atoms on both sides:
- Left side (Reactants): 1 Ba, 2 Cl, 2 Na, 1 SO₄
- Right side (Products): 1 Ba, 1 SO₄, 2 Na, 2 Cl (because of 2NaCl)
See how they match perfectly? We started with 2 chlorine atoms in BaCl₂, so we need 2 chlorine atoms on the product side too. That’s why we write 2NaCl – it gives us those 2 chlorine atoms. Simple as that.
Understanding the Second Equation: Sodium Hydroxide + Hydrochloric Acid
NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
This is your classic neutralization reaction – when an acid meets a base, they neutralize each other to form salt and water. You’ve probably done this in your lab with phenolphthalein indicator, right? The pink color disappears when neutralization is complete.
Good news here – this equation is already balanced! Let’s verify:
- Left side: 1 Na, 1 O, 2 H (1 from NaOH + 1 from HCl), 1 Cl
- Right side: 1 Na, 1 Cl, 2 H (both in H₂O), 1 O
Everything matches. Sometimes you get lucky and the equation balances itself naturally!
🔤 Understanding State Symbols (Don’t Skip This!)
State symbols tell us the physical state of each substance in the reaction. I’ve seen students lose marks just because they forgot these – don’t let that be you.
| Symbol | Meaning | Example from Our Equations |
|---|---|---|
| (s) | Solid | BaSO₄(s) – white precipitate that forms |
| (l) | Liquid | H₂O(l) – water in liquid form |
| (aq) | Aqueous (dissolved in water) | NaCl(aq), HCl(aq), NaOH(aq) – all dissolved |
| (g) | Gas | Not in these equations, but like CO₂(g) |
Why is BaSO₄ Solid While NaCl is Aqueous?
Great question! It’s all about solubility. Barium sulphate is practically insoluble in water – it immediately forms a solid precipitate that settles at the bottom. Sodium chloride, on the other hand, dissolves readily in water, so it stays in aqueous form. You can actually see this difference in your lab practical!
💡 Step-by-Step Balancing Strategy
Here’s how I teach my students to approach any chemical equation. Follow these steps and you won’t go wrong:
Step 1: Write the unbalanced equation with correct formulas
Don’t change the formulas! BaCl₂ is BaCl₂, not BaCl or BaCl₃. The formulas are fixed based on valency.
Step 2: Count atoms on both sides
Make a simple tally for each element. You can do this mentally or on paper.
Step 3: Balance one element at a time
Start with the most complex molecule or the one that appears least frequently. Use coefficients (numbers before formulas), never change subscripts.
Step 4: Verify your final equation
Count everything again – all atoms must match on both sides.
Step 5: Add state symbols
Think about what each substance is doing in the reaction. Is it dissolved? Is it a solid? Is it a gas?
📝 How to Write This Answer in Your Exam
⏱️ Time to Spend: 3-4 minutes (this is typically a 2-mark question)
Marking Breakdown:
- ✓ First balanced equation with state symbols – 1 mark
- ✓ Second balanced equation with state symbols – 1 mark
Step-by-Step Answer Format:
Step 1: Write a brief heading (optional but looks organized)
Write: “Balanced chemical equations with state symbols:”
Step 2: Write the first equation clearly
Write: (i) BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)
Step 3: Write the second equation
Write: (ii) NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
That’s it! Keep it simple and clear.
Must Include for Full Marks:
- ✅ Balanced equations (equal atoms on both sides)
- ✅ Correct chemical formulas
- ✅ State symbols for ALL substances
- ✅ Arrow (→) not equals sign (=)
- ✅ Coefficient “2” before NaCl in first equation
Don’t Make These Mistakes:
❌ Writing BaCl₂ + Na₂SO₄ → BaSO₄ + NaCl
→ This is unbalanced! You’ll lose marks.
✅ Must write 2NaCl to balance chlorine atoms
❌ Forgetting state symbols
→ Even if equation is balanced, you lose 0.5 marks
✅ Always include (s), (l), (aq), or (g)
❌ Writing H₂O(aq) instead of H₂O(l)
→ Water formed in neutralization is liquid, not aqueous
✅ Use (l) for pure water formed in reaction
Presentation Tips:
- • Write chemical formulas clearly – make subscripts small and obvious
- • Underline the final equations (makes them stand out)
- • Use (i) and (ii) to number the equations
- • Double-check your balancing before moving on
Quick Revision (Night Before Exam):
- • BaCl₂ + Na₂SO₄ needs “2” before NaCl
- • BaSO₄ is solid (s) – it precipitates
- • NaOH + HCl is already balanced (1:1:1:1 ratio)
- • Water formed is (l) not (aq)
- • Always count atoms to verify balance
⚠️ Common Mistakes Students Make
Mistake 1: Changing subscripts to balance
❌ Writing BaCl + Na₂SO₄ → BaSO₄ + NaCl (changing BaCl₂ to BaCl)
Why it’s wrong: You can’t change chemical formulas! They’re determined by valency.
✅ Correct approach: Only use coefficients (numbers before formulas) to balance.
Mistake 2: Confusing 2NaCl with Na₂Cl₂
❌ Thinking 2NaCl and Na₂Cl₂ are the same thing
Why it’s wrong: 2NaCl means two separate molecules. Na₂Cl₂ would be one molecule with 2 Na and 2 Cl bonded together (which doesn’t exist).
✅ Correct approach: Use coefficients before formulas, not subscripts within formulas.
Mistake 3: Using equals sign instead of arrow
❌ Writing BaCl₂ + Na₂SO₄ = BaSO₄ + 2NaCl
Why it’s wrong: Chemical equations use arrows (→) to show direction of reaction.
✅ Correct approach: Always use arrow (→) in chemical equations.
🔬 Lab Connection
You’ll actually perform the first reaction in your chemistry practical! It’s usually listed as Practical 2.2 or similar. When you mix BaCl₂ solution with Na₂SO₄ solution, you’ll immediately see a milky white precipitate forming – that’s your barium sulphate.
The second reaction – neutralization – you might demonstrate using phenolphthalein indicator. Add the pink NaOH solution to colorless HCl, and watch the pink color disappear as neutralization happens. It’s actually quite satisfying to see!
Why Balancing Actually Matters
You might be thinking, “Why all this fuss about balancing?” Here’s the thing – atoms don’t just disappear or appear out of nowhere during a reaction. That’s the law of conservation of mass in action.
Think of it this way: if you start with 2 chlorine atoms (from BaCl₂), you must end with 2 chlorine atoms. They just rearrange into different molecules. The total number stays the same.
This isn’t just academic stuff, by the way. Chemical engineers use balanced equations to calculate exactly how much of each reactant they need in factories. Too much or too little means wasted money or unwanted byproducts. So yeah, it’s pretty important in the real world too!
❓ Frequently Asked Questions
Q1. How do I know which state symbol to use?
A1. Look at the reaction conditions. If it says “solution” or “dissolved in water,” use (aq). If it mentions a precipitate or solid forming, use (s). Water formed in reactions is usually (l). Gases are obvious – they bubble out or escape, so use (g). With practice, you’ll develop an intuition for this.
Q2. Can I treat SO₄ as one unit when balancing?
A2. Yes! SO₄²⁻ is a polyatomic ion that stays together as a unit in these reactions. So you can count “1 SO₄” on each side rather than counting sulfur and oxygen separately. This makes balancing much easier.
Q3. What if I can’t balance an equation?
A3. Start over with a systematic approach. Balance metals first, then non-metals, then hydrogen, and oxygen last. If you’re still stuck, check if you’ve written the correct chemical formulas – that’s usually where the problem is. Also, make sure you’re using coefficients (numbers before), not changing subscripts.
Q4. Is the order of products important?
A4. Not really for correctness, but there’s a convention. In double displacement reactions, write the precipitate (solid) first, then the aqueous product. In neutralization, write salt first, then water. Following these conventions makes your answer look more polished and professional.
Q5. Will I lose marks if I forget state symbols?
A5. Yes, typically 0.5 marks per equation. Even if your equation is perfectly balanced, missing state symbols means incomplete answer. Since this question is usually worth 2 marks total, losing 0.5-1 mark for state symbols is significant. Always include them!
🔗 Related Questions You Should Study
- Chapter 2, Q1: Why should a chemical equation be balanced?
- Chapter 2, Q2: Translate word equations into balanced chemical equations
- Chapter 2, Q4: Write balanced equation for hydrogen + chlorine → hydrogen chloride
- Chapter 2, Q5: Balance: Ca(OH)₂ + HNO₃ → Ca(NO₃)₂ + H₂O
- Chapter 1 Review: Understanding chemical formulas and valency (prerequisite concept)
💡 Final Tip: Balancing equations might seem mechanical at first, but it’s actually quite logical once you get the hang of it. Practice 5-10 equations on your own, and you’ll develop an intuition for it. This question typically appears as a 2-marker in board exams – it’s basically free marks if you’ve practiced enough. Don’t lose points on something this straightforward!
📚 Reference: NCERT Class 10 Science Textbook, Chapter 2: Acids, Bases and Salts, Page 28
✍️ Content by: Educational Content Team | Reviewed by CBSE Educators